/*
 * Copyright 2009 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.gwt.event;

import com.google.web.bindery.event.shared.Event;

/**
 * Root of all GWT widget and dom events sourced by a {@link HandlerManager}.
 * All GWT events are considered dead and should no longer be accessed once the
 * {@link HandlerManager} which originally fired the event finishes with it.
 * That is, don't hold on to event objects outside of your handler methods.
 * <p>
 * There is no need for an application's custom event types to extend GwtEvent.
 * Prefer {@link Event} instead.
 *
 * @param <H>
 *            handler datyType
 */
public abstract class GwtEvent<H extends EventHandler> extends Event<H> {
	private boolean dead;

	/**
	 * Constructor.
	 */
	protected GwtEvent() {
	}

	@Override
	public abstract GwtEvent.Type<H> getAssociatedType();

	@Override
	public Object getSource() {
		assertLive();
		return super.getSource();
	}

	/**
	 * Asserts that the event still should be accessed. All events are
	 * considered to be "dead" after their original handler manager finishes
	 * firing them. An event can be revived by calling {@link GwtEvent#revive()}
	 * .
	 */
	protected void assertLive() {
		assert (!dead) : "This event has already finished being processed by its original handler manager, so you can no longer access it";
	}

	/**
	 * Should only be called by {@link HandlerManager}. In other words, do not
	 * use or call.
	 *
	 * @param handler
	 *            handler
	 */
	protected abstract void dispatch(H handler);

	/**
	 * Is the event current live?
	 *
	 * @return whether the event is live
	 */
	protected final boolean isLive() {
		return !dead;
	}

	/**
	 * Kill the event. After the event has been killed, users cannot really on
	 * its values or functions being available.
	 */
	protected void kill() {
		dead = true;
		setSource(null);
	}

	/**
	 * Revives the event. Used when recycling event instances.
	 */
	protected void revive() {
		dead = false;
		setSource(null);
	}

	void overrideSource(Object source) {
		super.setSource(source);
	}

	/**
	 * Type class used to register events with the {@link HandlerManager}.
	 * <p>
	 * Type is parameterized by the handler datyType in order to make the
	 * addHandler method datyType safe.
	 * </p>
	 *
	 * @param <H>
	 *            handler datyType
	 */
	public static class Type<H> extends com.google.web.bindery.event.shared.Event.Type<H> {
	}
}
